Various entities define levels of autonomy that classify vehicles according to how autonomously the vehicles can operate. For example, the National Highway Traffic Safety Administration (NHTSA) establishes five levels (0 to 4) and defines Level 2 autonomy as “automation of at least two primary control functions designed to work in unison to relieve the driver of control of those functions,” for example, “adaptive cruise control in combination with lane centering.” NHTSA defines Level 3 autonomy as “enabl[ing] the driver to cede full control of all safety-critical functions under certain traffic or environmental conditions and in those conditions to rely heavily on the vehicle to monitor for changes in those conditions requiring transition back to driver control,” for example, “signal[ing] to the driver to reengage in the driving task” in response to “an oncoming construction area.”
Similarly, the Society of Automotive Engineers (SAE) establishes six levels (0 to 5) and defines Level 2 autonomy as “the driving mode-specific execution by one or more driver assistance systems of both steering and acceleration/deceleration using information about the driving environment and with the expectation that the human driver perform all remaining aspects of the dynamic driving task.” SAE defines Level 3 autonomy as “the driving mode-specific performance by an automated driving system of all aspects of the dynamic driving task with the expectation that the human driver will respond appropriately to a request to intervene.”
During Level 2 or 3 autonomous driving under either set of definitions, a vehicle occupant is expected to maintain attention on the task of driving the vehicle while the vehicle performs many of the actions of the driving task and/or be prepared to take over operation of the vehicle. This is a problem particular to semi-autonomous vehicles. If the vehicle has full autonomy, then the occupant typically is not expected to maintain attention on the driving task. If the vehicle is nonautonomous, then the occupant is a driver is constantly performing actions to control the vehicle, which thus maintains the attention of the driver.